Metallurgy



Patented Feb. 27, 1945 UNITED STATES PATENT oFF ce METALLURGY Marvin J.Udy, Niagara Falls, N. Y.

No Drawing. Application January 8, 1942, Serial No. 426,046

4 Claims. (01. 75-176) iron and chromium such, for example, as low-.

carbon ferrochromium. A further object of the invention is to produceimproved ferro-alloy products comprising low-carbon ferrochromium.

The expression low-carbon ferrochromium, as herein employed is intendedto define crude alloys consisting essentially of iron and chromium andused chiefly to incorporate chromium in iron or steel, alloys of thetypes and compositions, for example, ofthose produced according toheretofore customary procedures by reducing chromite ore directly withcarbon to produce highcarbon ferrochromium. incorporating silicon in thehigh-carbon ferrochromium to remove carbon, and treating the resultingproduct with oxidizing material to remove excess silicon with theproduction of low-carbon ferrochromium containing chromium and iron insubstantially the same ratio as in the high-carbon ferrochromiumproduced initially.

According to some heretofore customary practices, ferro-alloys areproduced by reducing compounds of iron and alloying elements such, forexample, as chromium, silicon, manganese, vanadium, tungsten, titaniumand molybdenum at elevated temperatures in suitable furnaces with.

the production of molten baths of the ferro-alloys, the relativeproportions of iron and alloying elements in the final alloy productsbeing determined by the relative proportions of iron and the alloyingelements present in the furnace charges. The amount of ferro-alloy, orthe size of the molten bath of ferro-alloy, produced in any particularoperation is determined by the capacity of the apparatus employed.Ferro-alloys are produced, usually, in electric furnaces of thesubmerged arc type which operate continuously to produce ferro-alloysbut from which the ferroalloys are tapped intermittently at spaced timeintervals. The amount of ferro-alloy tapped from a furnace each time maybe small or large, depending upon the furnace construction and capacityand its operating characteristics.

Ferro-alloys are employed in industry in the form of solid pieces whichare relatively low in weight as compared with the weight of the moltenferro-alloy metal baths produced in the furnace operations. According tosome heretofore customary practices, solid pieces of ferro-alloy ofsizes useful in industry are produced by pouring the bulky or massivemolten alloy product of a furnace into a chill in the form of a shallowmetal'pan, permitting the molten metal to solidify, and breaking thesolidified massive metal products into smaller pieces, as, for example,pieces measuring about two to six inches in greatest diameter, by meansof hammers.

As produced in a properly operated furnace, the molten ferro-alloyproduct is of uniform composition throughout. As cooling and gradualsolidification take place in the chill, however, the composition of themetal product becomes nonuniform owing to the formation of compounds ofthe iron with the one or'more alloying elements present which havedifferent freezing temperatures. Thus, for example, iron and chromiumare capable of forming many compounds containing iron and chromium indifferent proportions and which freeze at different temperatures andsegregate as solidification of the molten product takes place slowly.When carbon is employed as the reducing agent, as in the case offerrochromium production, some carbon is present in the molten furnaceproduct and further infiuences segregation and the production ofnonuniform products by forming with iron and the one or more alloyingelements present compounds having different freezing temperatures. Theproportions of ironand alloying element in various portions of asolidified furnace. product may vary as much as ten percent or evenmore. Thus, for example, in a solidified mass of high-carbonferrochromium formed in a shallow chill, the material in the centralportion may contain about seventy percent of chromium, the material inthe outer portions may contain as little as sixty percent of chromiumand the material in the intermediate portions may contain chromium invarious amounts ranging from sixty to seventy percent.

Ferro-alloys are used largely for metallurgical purposes as additionagents for incorporating alloying elements in molten iron and steel toproduce iron and steel products of rather rigid specifications withrespect to contents of alloy elements. The non-uniform character of theproducts of ferro-alloy furnaces produced in accordance with heretoforecustomary practices has complicated the problem of adding ferro-alloysto iron and steel in proper amounts to meet rigid specifications withrespect to contents of alloy elements, and the production of iron andsteel products of proper compositions involves considerable difliculty.The problem of adding ferroalloys to iron and steel in proper amounts tomeet rigid specifications is complicated not only by the fact thatvarious portions of any particular solidified product of a furnace maybe of different compositions, but also, by the fact that products formedin and tapped from the same furnace at difierent times differ incompositions from one another as well as within themselves, since ashipment of ferro-alloy from a ferro-alloy producer to a steel plant foruse may be made up of products produced in and tapped from the furnaceat different times. Such shipments may be made up also of non-uniformproducts of several different furnaces. A single shipment of ferroalloymay be employed by the steelmaker as source of ferro-alloy for makingnumerous heats of alloy iron or steel over a substantial period of time.Various portions of a particular shipment may have widely differentchemical composi tions, and, consequently, the results obtained in theuse of a portion of a shipment of ferro-alloy for producing one heat ofiron or steel can not be relied upon when using another portion of thesame shipment to produce other heats of iron or steel.

The non-uniform character of commercial grades of ferro-alloys availableto producers of alloy iron and steel products is illustrated by thefollowing table appearing on page 20 of volume I of Alloys of Iron andChromium (McGraw Hill Book Company, Inc., New York, 1937) and settingforth typical analyses of various grades of ferrochromium:

Ferro-alloys such as ferrochromium products may be sold to the alloyiron or steel producer under specifications covering the relatively wideranges of percentages of all components or constituents illustrated bythe above table. Under the circumstances it is difiicult or impossiblefor an alloy iron or steel producer to predict accurately the finalcomposition of aproduct formed by adding to a molten metal bath aquantity of the ferro-alloy.

The present invention contemplates the elimination of difficultiesencountered heretofore in the incorporation of chromium in iron andsteel to meet rigid specifications with respect to chromium and carbon.

In accordance with the present invention, the massive product of theferro-alloy furnace producing low-carbon ferrochromium is so treated asto form a relatively finely divided product of substantially uniformchemical composition throughout. In a preferred method or process of theinvention, the molten product of a ferroalloy furnace is chilled rapidlyto a temperature below the freezing temperature of the lowestfreezing-point compound which might be formed by the components orconstituents of the ferroalloy. A final substantially uniform productformed in accordance with the invention may comprise low-carbonferrochromium obtained by tapping a single furnace one or more times orby tapping two or more similarly operated furnaces one or more timeseach.

Rapid chilling and granulating, or finely dividing, may be accomplishedin any suitable manner, as, for example, by directing a jet ofrelatively cold gas (such as steam or air) under pressure or liquid(such as water) against a.

stream of the molten ferrochromium or by pouring the molten ferrochromium into a large volume of water. Rapid chilling of a stream ofmolten ferrochromium results in the production of a relatively finelydivided or granulated solid product consisting of pieces or particlesall of which are of substantially the same chemical composition. Thesizes of the particles produced will be determined largely by the rateof chilling or by the relative proportions and temperatures of themolten ferrochromium and chilling agent.

For effective chilling and granulation of the ferrochromium, I maydirect one or more jets of cold water against a stream of theferrochromium as it pours from the furnace. Preferably, I pour themolten ferrochromium in such manner that the metalpasses downwardlythrough two or more vertically spaced streams of water flowingtransversely of the direction of flow or fall of the metal. The streamsof water preferably are formed by flowing the water under about fortypounds per square inch pressure, more or less, through nozzles havingsubstantially rectangular outlet orifices of such dimensions as to formfiat wide streams, that is, streams having greater horizontal thanvertical dimensions. The widths and depths of the streams of water willbe determined in each case by the size of the stream of metal and itsrate of flow. Granulation may be effected substantially entirely bychilling, or the pressure or force of the granulating fiuid employed maybe such that granulation is assisted also by mechanical disruption ofthe molten metal.

Products produced by granulation with water may be deposited directly onperforated conveyors to permit de-watering. The conveyors may carry theproducts to drying apparatus for final elimination of the water.

The granulating feature of the invention may surface of a slag coveredmolten bath of steel or iron, the particles of a uniform product formedin accordance with the invention may be too small to penetrate the slagsatisfactorily. In order to avoid difiiculties which might result insuch cases, I may bond together sufficient numbers of particles to formmasses of suitable sizes. The particles may be molded in any suitableshapes and sizes and bonded together by means of any suitable bondingagentunder such conditions as to produce dry, or water-free, solidproducts. Sodium silicate, Portland cement, sodium carbonate or sodiumnitrate or any combination of two or more of these substances may beemployed satisfactorily for bonding the particles.

When the ferrochromium is to be employed in solid reaction mixtures, thegranulated particles may be too large to permit sufficiently intimatecontact with other components of the reaction mixtures. In such cases, Imay subject the particles to a grinding treatment in a ball mill orother suitable apparatus to produce smaller particles of suitable sizes.Granulation with a chilling agent such, for example, as water followedby grinding may be employed advantageously to facilitate the productionof particles of very small sizes. Granulation with water is relativelyinexpensive and grinding is relatively costly. The use of granulation.with water in conjunction with grinding results in greater efficiency ata lower cost. Granulation in water followed by grinding also permits theproduction of very small particles of some chromium-bearing ferro-alloyswhich otherwise could not be ground to such small sizes at all, or, ifat all, only with the greatest difliculty. Thus, for example, low-carbonferrochromium containing substantially less than about five per cent ofsilicon can be ground in ball mills and similar apparatus to produceparticles small enough to pass a 100- mesh screen only with the greatestdifficulty when the pieces of ferrochromium subjected to the grindingtreatment initially are of the sizes of those available heretofore. Suchlow-carbon ferrochromium products can be granulated by treatment withwater to form particles ranging in size from about one-sixteenth inchand smaller to about one-quarter inch and most of which are smaller thanone-quarter inch. Such particles may be ground to produce particlessmall enough to pass a IOU-mesh screen with little or no difficulty.

Low-carbon ferrochromium products which may be employed moreadvantageously in the production of alloy steel and iron than productsformed heretofore may be produced by chilling and granulating the moltenferrochromium. When a, ferrochromium product to be produced, as, forexample, for making up a single shipment to a steel plant, is to includeferrochromium tapped from a furnace at different times or ferrochromiumproduced in two or more similarly operated furnaces, the finely dividedparticles, whether produced by chilling and granulation or by chillingand granulation followed by grinding, should be mixed intimately.Satisfactory intimate mixing can be achieved with particles producedsimply by chilling and granulating molten ferroalloy, but more effectiveintimate mixing can be achieved with the smaller particles which can beproduced by grinding of particles produced by chilling and granulation.

In forming uniform ferrochromium products comprising ferrochromiumtapped from the furnace at different times or produced in two or moresimilarly operated furnaces, I prefer to produce finely divided productsconsisting largely of particles small enough to pass a -mesh screen. I

Uniform ferrochromium products formed in accordance with the inventionmay be sold to steel manufacturers and employed in the manufacture ofsteel and iron products in granular or,

finely divided form or in agglomerated form, but I prefer to prepareuniform ferrochromium products for use by steel and iron manufacturersin the form of agglomerates comprising relatively small particles of theferrochromium products. Bonding of the particles of ferrochromiumproducts aids in preventing segregation of particles of differentcompositions in any particular batch of material and insures delivery tothe steel manufacturer of products of substantially uniform compositionthroughout and comprising units or agglomerates all of which are ofsubstantially the same composition. The production of agglomerates aidsproducers of alloy iron active material.

and steel products by providing masses of ferrochromium products ofsuitable sizes for penetrating slag layers overlying molten iron andsteel baths.

Asglomerates produced in accordance with the invention may consistessentially of finely divided low-carbon ferrochromium and bondingmaterial which is substantially inert or non-reactive with respect tothe ferrochromium or they may comprise finely divided ferrochromium andre- Agglomerates consisting essentially of ferrochromium andsubstantially inert or non-reactive bonding material can be employed toperform the same functions as those for which pieces of solid low-carbonferrochromium have been employed in accordance with heretofore customarypractices. Agglomerates of the invention may constitute exothermicreaction mixtures of the types of those described in my United StatesPatents Nos. 2,176,688. 2,243,783, 2,243,784, and 2,243,786, and in mycopending application Serial No. 303,363, filed November 8, 1939, inwhich the ferro-alloy i associated with one or more materials capable oireacting with one another or with a component of the ferro-alloy. Theinvention may be employed advantageously to produce exothermic reactionmixtures comprising a low-silicon silicide of an alloy metal such, forexample, as low-silicon ferrochrome silicon (or high-siliconferrochromium) containing not more than about five percent of siliconand oxidizing material, such as sodium nitrate, capable of reacting withthe silicon of the ferrochrome silicon to generate heat for melting theiron and chromium. Such reaction mixtures require ferrochrome silicon inthe form of small particles, preferably small enough to pass a 100-meshscreen, and, as hereinbefore pointed out, particles of such small sizeare difficult to produce by direct grinding but can be produced quiteeasily by water chilling and granulation followed by grinding.

I claim:

1. In the production of a ferro-alloy product suitable for use a anaddition agent for incorporating an alloying element in molten iron orsteel, the improvement which comprises finely dividing low-carbonferrochromium by chilling and granulating from the molten state andforming a product comprising solid particles of low-carbon ferrochromiumand of substantially uniform chemical composition.

2. In the production of a ferro-alloy product suitable for use as anaddition agent for incorporating an alloying element in molten iron orsteel, the improvement which comprises finely dividing low-carbonferrochromium by chilling and granulating from the molten state withwater and forming a product comprising solid particles of low-carbonferrochromium and of substantially uniform chemical composition.

3. A product suitable for use as an addition agent for incorporatingchromium in molten iron or steel comprising solid particles oflow-carbon ferrochromium formed by chilling and granulating moltenlow-carbon ferrochromium.

4. A product suitable for use as an addition agent for incorporatingchromium in molten iron or steel comprising solid particles oflow-carbon ferro-chromium formed by chilling and granulating moltenlow-carbon ferrochromium with

